Report brings climate change home

Climate change is here now and will get worse unless we do everything we can to curb greenhouse gas emissions. That's the message in a report published today by the Royal Society of New Zealand.

The report confirms the severity of local threats from climate change, which include more frequent coastal and river floods, fires and droughts. It identifies six areas where New Zealand would be most directly affected, says Victoria University climate scientist James Renwick, who chaired the expert panel that wrote the report.

He says the impacts are set to get worse as climate change accelerates over the coming decades “unless significant action is taken to reduce global emissions of greenhouse gases”.

As every consecutive month this year has broken the temperature record globally, the report draws on research and climate models to describe what this means locally, including more frequent extreme weather, more communities at risk from damaging floods and droughts, distorted ecosystems on land and in the ocean, climate-driven extinctions, and disrupted trade relations.

“We can already see climate change affecting New Zealand, and how much worse it gets really depends on what we do in the short term, over the next few years,” says Professor Renwick. “When you look at the risks it’s clear that this is an urgent issue.”

Professor Renwick says New Zealand will likely exceed the global average, which will cause coastal erosion and flooding, especially when combined with storm surges. “Many New Zealanders live on the coast and two-thirds of us live in flood-prone areas so we are vulnerable to these projected changes.”

Even small changes in average conditions can bring large changes in the frequency of extreme events, he says. “With a 30cm rise in sea level, the current 1-in-100-year extreme sea event would be expected to occur once every year or so in many coastal regions. Along the Otago coast for example, the difference between a two-year and 100-year storm surge is about 32cm of sea level.”

Rising seas also lift the water table, leading to frequent or even permanent flooding of low-lying areas, and the potential for salt water to contaminate freshwater systems.

While the implications will vary widely along New Zealand’s coastline, Professor Renwick says thousands of households will be affected and will need to decide whether “to hold the line or to relocate in response to known risks”.

The report highlights that episodes of extreme coastal flooding are already occurring, such as recurring flooding of Auckland’s north-western motorway and Tamaki Drive at times when storm surges coincide with king tides.

Several regional authorities are already grappling with how to prepare for ongoing sea-level rise, but some have faced legal action from residents living near the coast. Without clear legislative guidance, the report says, such litigation is likely to increase.

As the atmosphere warms, it holds more water, which means that extremely heavy rains are expected to become more frequent in most parts of the country, by a factor of up to four.

Some recent floods, for example the intense rainfall in Golden Bay in 2011, have already been partly attributed to climate change, the report says.

As rising seas bring more coastal flooding and heavy downpours swell rivers, the combination of both means that river mouths will be particularly vulnerable.

“It’s another big issue,” says Professor Renwick. “Do we have ways of protecting ourselves against those things by, for instance, building large stop banks, or do we have to think hard about whether we live where we’re living at the moment.”

Less rain in the east and north, in combination with higher temperatures, will increase the frequency and intensity of droughts, while at the same time, fire risk is expected to go up. “The number of days with very high and extreme fire weather is expected to increase, with the greatest changes in the east and north of both islands.”

“Changes in ocean temperature, water chemistry and currents will have impacts on New Zealand’s marine life … including southward migration of species and negative effects on shell-forming species such as paua and mussels.”

A 15-year time series taken off the Dunedin coast shows that the ocean around New Zealand is acidifying in consistence with global changes, and the projection is that this will continue, together with ongoing warming, leading to disrupted marine ecosystems and productivity.

“Our societies are not designed to cope with such rapid change,” the report says. “Ultimately, how the future plays out depends critically on significantly cutting emissions of greenhouse gases to below 2ºC.”